chemical engineering problems

1. Sulfate (molecular weight = 96g/mole) from an acid mine treatment pond leaves via an

outlet stream at a concentration of 275 mg/L. The outlet stream flows into a small river

with a flow of 30 cfs upstream, 37 cfs downstream, and a background sulfate

concentration of 17 mg/L. Please answer the following.

a. What is the concentration of outlet stream sulfate in moles/L and equivalents/L?

b. What is the concentration of sulfate in the river immediately downstream of the

confluence with the outlet stream in mg/L?

2. One oxidation treatment process uses light and hydrogen peroxide to generate the

highly reactive hydroxyl radical (OH•), which can be used to degrade certain PFAS

“forever compounds”, but not others. A very recent paper by Zhang (2023

Environmental Science and Technology: so recent no volume has been assigned) report a

second order rate constant between OH• and the PFAS, perfluoro(2-

ethoxyethane)sulfonic acid (PFSA with a k = 1.2 x 10 7 L/mole-second), while this radical is

less reactive with 4.8-dioxa-3H-perfluorononanoic acid (DPFA with a k = 5 x 10 5 L/mole-

second). Suppose your UV-hydrogen peroxide system generates a constant output

(steady-state) of this radical at a concentration of 3 x 10 -14 moles/L, please answer the

following.

a. What is the pseudo-first order rate constant for the degradation of both

compounds at this OH• concentration?

b. What are the half-lives for these two compounds?

c. Suppose you have to treat these two compounds such that they both must not

exceed the 50 nM water quality standard. If both compounds have a starting

concentration of 1µM how long (in hours) will it take each to reach this

concentration? For the slower reacting compound is the time needed to achieve

the water quality standard a reasonable time from a design perspective?